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Background: Plants can directly affect litter decomposition by producing litter materials of different qualities. However, whether living plants have indirect effects on litter decomposition by affecting changes in forest microenvironments is presently unclear in plantation forests. Methods: We addressed this issue by studying the decomposition of the leaf litter and fine roots of Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.], a timber species widely planted in China, in 113 non-neighboring quadrats of varying basal area of the dominant plant species (i.e., Chinese fir) and distinct basal areas and species richness of regenerated woody plants (i.e., species other than Chinese fir) in a subtropical Chinese fir forest. Results: Our results showed that fine roots decomposed significantly more rapidly than leaf litter possibly because fine roots were easier access to mineralized nutrients and microbes compared with leaf litter. Further analyses showed that leaf litter and fine root decomposition rates were significantly controlled by the plant community attributes. The decomposition of both leaf litter and fine roots was mainly controlled by woody species regenerated during stand development rather than by Chinese fir. Specifically, leaf litter and fine root decomposition rates decreased with increasing basal area of regenerated woody plants, possibly due to nutrient competition and/or reduced photodegradation. Conclusions: This study provides empirical evidence that woody species regenerated during stand development play a certain role in determining litter decomposition rates through plant-soil interactions in Chinese fir plantations. Regenerated woody plants should be considered in future studies on soil carbon and nutrient cycling in plantation forest. [ABSTRACT FROM AUTHOR]

Background and aims: Atmospheric nitrogen (N) deposition alters the priming effect (PE), which is defined as the change in native soil organic carbon (SOC) decomposition by exogenous C inputs. However, how the priming intensity varies under chemically heterogeneous N deposition, particularly with increasing labile C input, remains unclear. Methods: We collected soils from a temperate forest in northeastern China that had received simulated organic and/or inorganic N deposition for 6 years. The soils were incubated with or without three levels of 13C-labelled glucose solution for 152 days. CO2 emission and its 13C value were continuously measured to calculate the PE. Results: Enhanced SOC decomposition (i.e., a positive PE) was observed after glucose addition, regardless of the N deposition form. The PE intensity increased with the increase in the glucose addition level. However, organic N decreased the PE by 12.3-23.2%. The SOC-derived microbial biomass was 16.2-34.3% lower in organic N-treated soil, indicating that preferential utilization of exogenous labile C by microorganisms was responsible for the decrease in PE. The PE inhibition by organic N increased nonlinearly as a function of glucose level. Furthermore, the net annual change in SOC as a balance between the replenishment of added glucose-C and primed C was larger in organic N-treated soil due to a decrease in soil microbial metabolic quotient. Conclusions: In this study, we found that organic N deposition inhibited the PE, and the inhibition effect was intensified with increasing C inputs, favouring SOC sequestration. [ABSTRACT FROM AUTHOR]

Background and aims: Priming effect (PE) of soil organic carbon (SOC) decomposition induced by exogenous organic C is an important ecological process in regulating the soil C cycle. The objective of this study was to evaluate how the PE varied among different ecosystems at the global scale and explore factors that drive the direction and magnitude of the PE. Methods: Using 2048 experimental comparisons compiled from 94 incubation studies with stable (13C) or radioactive (14C) carbon isotopic techniques, we performed a meta-analysis on the effect of exogenous organic C input on native SOC decomposition (i.e., PE) across multiple terrestrial ecosystems. In particular, the linear mixed-effect model was used to examine the relationship between the PE and potential influencing factors. Results: The addition of exogenous organic C significantly enhanced native SOC decomposition by 47.5% (i.e., positive PE), with the highest value in cropland soils (60.9%) and the lowest value in forest soils (26.2%). The intensity of the PE decreased with increasing SOC content, soil total nitrogen content, soil C/N, incubation duration, and incubation temperature, but increased with increasing exogenous organic C addition rate and soil pH. Soil PE was not affected by the complexity of exogenous organic C. Conclusions: Our results indicate that positive PE is a widespread phenomenon in terrestrial ecosystems, and that the magnitude is closely related to soil properties and experimental conditions. These findings may be useful for understanding soil C priming and the effect on soil C balance under climate change scenarios. [ABSTRACT FROM AUTHOR]

Background and aims: The canopies in evergreen coniferous plantations are often composed of various-aged needles. Plantation management, such as thinning, produced abundant harvest residue, including needles with different needle ages. However, little attention was paid to the effect of needle age on decomposition, although the needle chemical properties varied substantially with leaf ages.Methods: A field experiment was conducted for 3 years to investigate the decomposition of harvest residue needles at different needle ages, and determine the main controlling factors in different stages of decomposition in a Chinese fir plantation.Results: We found that the initial decomposition rate varied 5-fold among different needle ages in a Chinese fir plantation. Litter quality controlled the overall litter decomposition rate, especially the initial decomposition rate. Needle nitrogen content was positively correlated to decomposition rate during the early stage of decomposition. However, it was negatively correlated to decomposition rate during the later stage of decomposition. The contents of needle tannins increased the asymptotic mass remaining (A, proportion of mass remaining at which decomposition approaches zero, i.e., the fraction of slowly decomposing litter). We also found that the initial litter decomposition rates in soil fauna presence were significantly higher than those in soil fauna absence across different needle ages. Moreover, the effect of soil fauna on initial litter decomposition is independent of needle quality.Conclusions: Our results suggest that needle age and plant secondary metabolites should be considered to understand the response of litter decomposition and nutrient cycling to management practices, such as thinning, in conifer plantations. [ABSTRACT FROM AUTHOR]

Aims: Changing quantity and quality of plant C input to soils under global change influences soil C cycling in terrestrial ecosystems. However, how soil CO emission responds to changes in C input remains poorly understood. Methods: A detritus input and removal experiment was conducted in a subtropical forest ( Cunninghamia lanceolata) to investigate how aboveground and belowground litters affect soil respiration (R). In this experiment, four treatments with three replicates were included, as follows: control (CK), litter removal (NL), root trenching (NR), and no C-input (i.e. litter removal combined with root trenching, NI). R was measured for 4 years from 2011 to 2014. Results: The mean annual CO effluxes in the NL, NR, and NI plots were lower (23.4%, 24.9%, and 38.8%, respectively) than those in the CK plots, suggesting that decreasing C input significantly decreased R. Soil heterotrophic respiration (soil organic matter decomposed by microorganisms) accounted for 52.1% of R, and aboveground recent litter decomposition and belowground autotrophic respiration (live roots and associated microorganism) contributed to 23.7% and 24.2% of R, respectively. R was significantly and positively correlated with soil temperature, but negatively correlated with volumetric soil moisture. The variation in R was more explained by soil temperature than soil moisture, and the responses of R to soil temperature and moisture were altered by C input manipulation. Annual R rate was strongly and negatively related to the Gram-positive bacteria concentration and the ratio of Gram-positive to -negative bacteria. Conclusion: This study highlighted that aboveground recent leaf litter and belowground live roots and associated microbes had similar contributions to R, and soil temperature and Gram-positive bacteria were the dominant factors controlling R in a subtropical forest. [ABSTRACT FROM AUTHOR]

Background and Aims: Root branching leads to morphological and functional heterogeneity of fine roots. However, the structure of soil microbiota associated with root branching orders has never been investigated. Deep insights into rhizosphere microbial community could provide a better understanding of the plant-microbe relationship. Methods: Fine roots of poplar ( Populus × euramericana (Dode) Guinier.) were sampled and sorted into three groups according to their branching orders. Scanning electron microscopy (SEM) was used to observe the surface features of different orders of fine roots. Illumina MiSeq was employed to analyze the bacterial community structure of soil compartments from different root orders (i.e., R1, R2, and R3) and bulk soil compartment (NR). Results: SEM showed that the first-order root with smaller diameter had dense coverage of vigorous root hairs, whereas higher order roots with larger diameter had sloughed-off cortical tissues on the rhizoplane. The diversity of bacterial communities was higher in the R1 and R2 compartment than in R3 or NR. There were 80 genera with a relative abundance above 0.05% in soils. Ternary plot revealed that bacterial genera were significantly enriched in R1 than in R2 or R3. Redundant analysis (RDA) showed that 12 dominant bacterial genera with a relative abundance over 1% were significantly correlated with P and NH -N content of soils. Conclusions: Root orders could influence the inhabitation of bacterial communities. The core groups of bacterial communities inhabiting the rhizosphere were correlated with soil nutrients. The root order-dependent interactions of plant-microbe provided a new model about the association between roots and soils. [ABSTRACT FROM AUTHOR]